Evaluating Reintroduction Strategies for Redfish Lake Sockeye Salmon Captive Broodstock Progeny
J. Lance Hebdon, Paul Kline, Doug Taki, and Thomas A. Flagg
Abstract.—Snake River sockeye salmon Oncorhynchus nerka were listed as endangered in 1991. Prior to listing, a captive broodstock program was initiated to prevent species extinction and to begin rebuilding the population. Reintroduction plans for captive broodstock progeny have followed a “spread-the-risk” philosophy incorporating multiple release strategies and lakes. Since 1993, more than 860,000 presmolts, 158,000 smolts, 325,000 eyed eggs and 880 adults have been reintroduced to the habitat. From this production, 312 anadromous sockeye salmon have returned to adult trapping facilities in the Sawtooth Valley of Idaho. Monitoring and evaluation efforts have focused on maximizing the use of limited hatchery-rearing space and on identifying and prioritizing the most successful reintroduction strategies. Comparisons of presmolt overwinter survival and out-migration success from nursery lakes have shown that (1) presmolts released directly to Redfish Lake in October have emigrated more successfully than presmolts reared in Redfish Lake net pens prior to release, (2) presmolts released directly to Alturas and Pettit lakes in October have emigrated more successfully than presmolts released directly to lakes in July, and (3) presmolts reared at the Idaho Department of Fish and Game (IDFG) Sawtooth Fish Hatchery emigrated more successfully than presmolts reared at the IDFG Eagle Fish Hatchery following July releases to Alturas and Pettit lakes. Presmolts that spent one winter in Redfish Lake prior to out-migration were interrogated more successfully at lower Snake and Columbia River dams than smolts released in the outlet of Redfish Lake. Smolt-to-adult return rates for anadromous adults produced by the captive broodstock program from 2000 to 2002 varied from 0.6% for unmarked fish returning in 2002 to 0.4% for a combined smolt and presmolt release group in 2000. Using captive broodstock techniques, the program has successfully prevented the extinction of Snake River sockeye salmon and increased population abundance in the habitat. However, without substantive improvements in smolt-to-adult survival, program efforts will likely be insufficient to rebuild the population to self-sustaining levels.